1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices using a silicone protective layer which is capable of serving as a stress relaxation protective layer for the semiconductor devices.
2. Description of the Related Art
Hitherto, as published in 7, 9-15 (1983) "Kino Zairyo (functional material)" or 51, No. 7, 554-558 (1983) "Denki Kagaku (electro chemistry)", polyimide materials have been used as a stress relaxation protective layer of the type to be provided for semiconductor devices such as EPROMs. Such polyimide materials exhibit an easy film forming possibility and form protective layers having an excellent heat resistance. However, the polyimide materials produce, as shown in FIGS. 1 (A) to (I), a problem in the manufacturing process for semiconductor devices because that manufacturing process for forming circuit patterns, such as bonding pads, is involved and too complicated.
FIGS. 1 (A) to (I) are cross-sectional views illustrating the steps of a process included in a manufacturing process for the semiconductor devices in which a stress relaxation protective layer is formed and pad apertures used for wire-bonding the aluminum circuit are bored by the conventional methods. In that conventional method, as shown in FIG. 1 (A), a resist 4 is applied to a silicon substrate 1 on which an aluminum circuit 2 has been disposed and covered by the glass coat layer 3. Next, as shown in FIGS. 1 (B) to 1 (D), the resist 4 is patterned, and the glass coat layer 3 is etched by a dry treatment using a plasma of the gas obtained by mixing carbon tetrafluoride and oxygen. Then, the resist 4 is removed by a dry treatment using an oxygen plasma.
Next, as shown in FIG. 1 (E), a stress relaxation protective layer 55 comprising a polyimide material is formed on the circuit 2 and the glass coat layer 3. Then, as shown in FIGS. 1 (F) and (G), another resist 4 is applied for the purpose of forming the pad apertures, and is patterned. Next, as shown in FIGS. 1 (H) and (I), the stress relaxation protective layer 55 is etched using an alkali solution, and the resist 4 is removed by a wet treatment using a solvent such as acetone and n-butyl acetate so that the pad is formed.
In the conventional method, patterning of the resist 4 needs to be conducted twice. This is because the stress relaxation protective layer 55 which is formed after the glass coat layer 3 has been etched also needs to be etched. As shown in FIG. 2 in which the present invention is illustrated as described later, if the glass coat layer 3 can be etched with the stress relaxation protective layer 5 used as a mask, the number of resist patterning steps can be reduced to one. However, as described above, the stress relaxation protective layer 55 generally comprises a polyimide material. Therefore, a problem arises in that the surface of the polyimide stress relaxation protective layer 55 can be degenerated by the plasma of a mixed gas formed by carbon fluoride and oxygen used to etch the glass coat 3. Another problem arises in that an oxygen plasma treatment which can be easily performed cannot be applied to an operation for removing the resist used for pattern-forming the stress relaxation protective layer 55. The reason for this is that polyimide materials can be incinerated during the oxygen plasma treatment. Furthermore, since even the silicone materials can crack when an oxygen plasma treatment is applied thereto, a wet treatment needs to be used for removing the resist but cannot easily be carried out.